1. Field of the Invention
This invention relates in general to spin valve magnetoresistive sensors for reading information signals from a magnetic medium and, in particular, to a spin valve sensor with high resistance magnetic layers adjacent to the magnetic shields to improve insulation of the magnetoresistive sensor from the conductive shields.
2. Description of the Related Art
Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive (MR) read sensors, commonly referred to as MR sensors, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater track and linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an xe2x80x9cMR elementxe2x80x9d) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which an MR element resistance varies as the square of the cosine of the angle between the magnetization in the MR element and the direction of sense current flowing through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers.
GMR sensors using only two layers of ferromagnetic material (e.g., Nixe2x80x94Fe) separated by a layer of non-magnetic material (e.g., copper) are generally referred to as spin valve (SV) sensors manifesting the SV effect.
FIG. 1 shows a prior art SV sensor 100 comprising end regions 104 and 106 separated by a central region 102. A first ferromagnetic layer, referred to as a pinned layer 120, has its magnetization typically fixed (pinned) by exchange coupling with an antiferromagnetic (AFM) layer 125. The magnetization of a second ferromagnetic layer, referred to as a free layer 110, is not fixed and is free to rotate in response to the magnetic field from the recorded magnetic medium (the signal field). The free layer 110 is separated from the pinned layer 120 by a non-magnetic, electrically conducting spacer layer 115. Hard bias layers 130 and 135 formed in the end regions 104 and 106, respectively, provide longitudinal bias for the free layer 110. Leads 140 and 145 formed on hard bias layers 130 and 135, respectively, provide electrical connections for sensing the resistance of SV sensor 100. IBM""s U.S. Pat. No. 5,206,590 granted to Dieny et al., incorporated herein by reference, discloses a GMR sensor operating on the basis of the SV effect.
FIG. 2 shows a prior art read back head 200 incorporating an SV sensor. Referring to FIG. 2, the spin valve sensor 100 is sandwiched between nonmagnetic insulative first and second read gap layers 202 and 204, and the read gap layers are sandwiched between ferromagnetic first and second shield layers 206 and 208. The separation between the first and second shield layers 206 and 208 defines the read gap 210. The ferromagnetic first and second shield layers 206 and 208 are needed to shield the sensor 100 from stray magnetic fields. The nonmagnetic insulative first and second read gap layers 202 and 204 provide electrical insulation of the sensor 100 from the metallic ferromagnetic shield layers 206 and 208.
A problem with the prior art sensors arises as the size of the read head is decreased in order to address the need for higher storage density disk files. As the read gap is made ultrathin, the insulative properties of the first and second read gap layers is reduced leading to possible shorting of the magnetoresistive sensor to the metallic shields. Therefore there is a need for improved insulation of the read sensor from the shields for read heads having ultrathin magnetic read gaps in order to read magnetic data at higher storage densities.
Accordingly, it is an object of the present invention to disclose a magnetic read head having ultrathin read gap layers with improved insulative properties between a magnetoresistive sensor and ferromagnetic shield layers.
It is another object of the present invention to disclose a magnetic read head having improved electrical insulation of the magnetoresistive sensor from the shields without increasing the magnetic read gap.
It is a further object of the present invention to disclose a magnetic read head having reduced smearing and telegraph noise by keeping metallic parts of the shields at an increased distance from the magnetoresistive sensor.
In accordance with the principles of the present invention, there is disclosed a preferred embodiment of the present invention wherein first and second shield cap layers made of high resistivity permeable magnetic material are formed between the first and second ferromagnetic shields and the first and second insulative read gap layers, respectively, of a magnetoresistive read head. In the preferred embodiment, the read head comprises a first shield cap layer of iron hafnium oxide (Fexe2x80x94Hfxe2x80x94Ox), or alternatively, manganese zirconium ferrite (Mnxe2x80x94Zn ferrite) disposed between the first ferromagnetic shield and the first insulative read gap layer, a spin valve sensor sandwiched between the read gap layer and a second insulative read gap layer, and a second shield cap layer of Fexe2x80x94Hfxe2x80x94Ox, or alternatively, Mnxe2x80x94Zn ferrite disposed between the second read gap layer and a second ferromagnetic shield.
The Fexe2x80x94Hfxe2x80x94Ox material, or alternatively, the Mnxe2x80x94Zn ferrite material provide highly resistive or insulating soft ferromagnetic layers which add to the electrically insulative read gap layers to provide increased electrical insulation of the spin valve sensor from the metallic ferromagnetic shields while not adding to the magnetic read gap of the read head. The extra insulation provided by the highly resistive shield cap layers makes it possible to use ultrathin insulative first and second gap layers without increased risk of electrical shorting between the spin valve sensor and the ferromagnetic first and second shields.
The above, as well as additional objects, features and advantages of the present invention will become apparent in the following detailed written description.